This invention relates in general to electrophotography and, more specifically, to an imaging member including an adhesive layer containing for example a copolyester-polycarbonate resin, and processes for fabricating the imaging member.
In electrophotography, an electrophotographic substrate (also referred to as a support or substrate support) containing a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging the surface. The plate is then exposed to a pattern of activating electromagnetic radiation, such as light. The light or other electromagnetic radiation selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the electrophotographic plate to a support such as paper. This image developing can be repeated as many times as necessary with reusable photoconductive insulating layers. The electrophotographic substrate is often referred to in the art as a electrophotographic imaging member, an electrostatographic imaging member, a photoconductive imaging member, a photoreceptor, a photoconductor, or the like.
Electrophotographic imaging members are well known. Typical electrophotographic imaging members include photosensitive members (photoreceptors) that are commonly utilized in electrophotographic (xerographic) processes in either a flexible belt or a rigid drum configuration. The electrophotographic imaging member may also be a flexible intermediate transfer belt. The flexible belt may be seamless or seamed. These belts are usually formed by cutting a rectangular sheet from a web, overlapping opposite ends, and welding the overlapped ends together to form a welded seam. These electrophotographic imaging members include a photoconductive layer having a single layer or composite layers. One type of composite photoconductive layer used in xerography is illustrated in U.S. Pat. No. 4,265,990, which describes a photosensitive member having at least two electrically operative layers.
An electrophotographic imaging member may take one of many different forms. For example, layered photoresponsive imaging members are known in the art. U.S. Pat. No. 4,265,990 describes a layered photoreceptor having separate photogenerating and charge transport layers. The photogenerating layer is capable of photogenerating holes and injecting the photogenerated holes into the charge transport layer. Thus, in photoreceptors of this type, the photogenerating material generates electrons and holes when subjected to light. More advanced photoconductive receptors contain highly specialized component layers. For example, a multilayered photoreceptor that can be employed in electrophotographic imaging systems can include one or more of a substrate, an undercoating layer, an optional hole or charge blocking layer, a charge generating layer (including photogenerating material in a binder) over the undercoating and/or blocking layer, and a charge transport layer (including charge transport material in a binder). Additional layers such as an overcoating layer or layers can also be included. See, for example, U.S. Pat. Nos. 5,891,594 and 5,709,974.
As more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, degradation of image quality was encountered during extended cycling. Moreover, complex, highly sophisticated, duplicating and printing systems operating at very high speeds have placed stringent requirements, including narrow operating limits, on photoreceptors. For example, the numerous layers found in many modern photoconductive imaging members must be highly flexible, adhere well to adjacent layers, and exhibit predictable electrical characteristics within narrow operating limits to provide excellent toner images over many thousands of cycles.
One type of multilayered photoreceptor that has been employed as a belt in electrophotographic imaging systems includes a substrate, a conductive layer, a blocking layer, an adhesive layer, a charge generating layer, and a charge transport layer. This photoreceptor may also include additional layers such as an anti-curl backing layer and an overcoating layer. Although excellent toner images may be obtained with multilayered belt photoreceptors, it has been found that the numerous layers limit the versatility of the multilayered belt photoreceptor. For example, there is a great need for long service life flexible photoreceptors in compact imaging machines that employ small diameter support rollers for photoreceptors belt systems fitted into a very confined space. Small diameter support rollers are also highly desirable for simple, reliable copy paper stripping systems which utilize the beam strength of the copy paper to automatically remove copy paper sheets from the surface of a photoreceptor belt after toner image transfer. Unfortunately, small diameter rollers, e.g., less than about 0.75 inch (19 mm) diameter, raise the threshold of mechanical performance criteria to such a high level that spontaneous photoreceptor belt material failure becomes a frequent event for multilayered belt photoreceptors. Thus, in advanced imaging systems utilizing multilayered belt photoreceptors, cracking has been encountered in one or more critical photoreceptor layers during belt cycling over small diameter rollers. Cracks developed in charge transport layers during cycling were manifested as print-out defects which adversely affected copy quality. Frequent photoreceptor cracking has a serious impact on the versatility of a photoreceptor and reduces its practical value for automatic electrophotographic copiers, duplicators, and printers.
Moreover, seams in multilayered belt photoreceptors tend to delaminate during extended cycling over small diameter support rollers. Seam delamination is further aggravated when the belt is employed in electrophotographic imaging systems utilizing blade cleaning devices. In addition, belt delamination is encountered during web slitting operations to fabricate belt photoreceptors from wide webs. Alteration of materials in the various belt layers such as the conductive layer, blocking layer, adhesive layer, charge generating layer, and/or the charge transport layer to reduce delamination is not easily effected because the new materials may adversely affect the overall electrical, mechanical, and other properties of the belt, such as residual voltage, background, dark decay, flexibility, and the like.
Interfacial adhesive layers have been used in order to maintain mechanical strength of various multilayered electrophotographic imaging members. Typical interfacial adhesive layer materials include, for example, polyesters, MOR-ESTER(copyright) 49,000 (available from Morton International, Inc.) (also referred to a xe2x80x9cMORTON(copyright) 49,000,xe2x80x9d xe2x80x9cMORTON(copyright) 49K,xe2x80x9d and xe2x80x9c49Kxe2x80x9d), VITEL(copyright) PE1100 (available from Bostik, Inc.), polyurethanes, and the like. Satisfactory results may be achieved with adhesive layer thickness between about 0.05 micrometer (500 angstroms) and about 0.3 micrometer (3,000 angstroms). Conventional techniques for applying an adhesive layer coating mixture to the charge blocking layer include spraying, dip coating, roll coating, wire wound rod coating, gravure coating, BIRD(copyright) applicator coating, and the like. Drying of the deposited coating may be effected by any suitable conventional technique, such as by oven drying, infra red radiation drying, air drying, and the like.
MORTON(copyright) 49,000 is a linear saturated copolyester reaction product of four diacids and ethylene glycol, in that it consists of alternating monomer units of ethylene glycol and four randomly sequenced diacids. MORTON(copyright) 49K has a weight average molecular weight of about 70,000 and a Tg of about 32 degrees C. It is believed that the presence of the diacids containing alkylene groups in MORTON(copyright) 49,000 linear saturated copolyester adhesive layers contribute to the delamination of multilayered photoreceptors during transport over small diameter rollers.
The present invention relates to an imaging member comprising, for example, at least a support, a charge blocking layer, an interfacial adhesive layer including a copolyester-polycarbonate resin, and a charge imaging layer. The copolyester-polycarbonate resin includes at least a copolymer of bisphenol-A and a phthalic acid dichloride ester. Other layers may be incorporated into the imaging member of the present invention in embodiments thereof, including, without limitation, undercoatings, conductive coatings, underlayers, ground strip layers, blocking layers, anti-curl layers, overlayers, and the like.
The present invention also involves a process for fabricating imaging members. The process comprises, for example, providing a support, providing a charge blocking layer, providing a charge imaging layer, and forming an interfacial adhesive layer between the charge blocking layer and the charge imaging layer. The interfacial adhesive layer may or may not be in direct contact with either the charge blocking layer or the charge imaging layer.
One advantage of the present invention in embodiments thereof is the provision of an increase in the adhesive bond strength of the interfacial adhesive layer, which is achieved substantially without negatively impacting the overall electrical properties of the imaging member.